1. Field of the Invention
This invention relates to dental instrumentation devices, and more particularly, to a system for allowing the display and recording of mandibular movement with a greater degree of accuracy than has been heretofore possible.
2. Description of the Prior Art
A kinesiograph mandibular tracker is a dental instrument used to measure and record mandibular movement which is sold by Myo-tronics Research, Inc., of Seattle, Wash. The kinesiograph mandibular tracker, which is described and claimed in U.S. Pat. No. 3,822,694, utilizes an array of sensors to measure the position of a magnet affixed to the lower incisors of the patient's mandible. The kinesiograph mandibular tracker uses these sensor outputs to generate signals representing frontal, sagittal and horizontal mandibular movement, and displays these signals on the face of a cathode ray tube. The kinesiograph mandibular tracker thus easily and quickly provides the kind of factual information needed to determine and diagnose occlusal problems.
Although the kinesiograph mandibular tracker has been advantageously used for many years with great success, the accuracy of the displayed position information is nevertheless limited by geometric distortions inherent in the arrangement of the sensor array. The sensors in the array generate outputs which are proportional to the distance between the sensor and the magnet affixed to the patient's mandible. The sensors thus accurately measure movement of the mandible when the mandible is moving directly toward and away from the sensor. However, mandible movements which are not directly toward and away from the sensor are not accurately measured. In other words, the sensors measure the vector component toward and away from the sensors, which differs from the actual movement vector when the vector contains components perpendicular to a line extending between the sensor and the magnet. The accuracy of the device is also affected by pure rotational movements of the magnet which alter the strength of the magnetic field at the sensor and are thus erroneously perceived as movements of the magnet. Another component of distortion is the slight degree of non-parallelism between the flux lines of the magnet and each sensor. Consequently, the conventional kinesiograph mandibular tracker displays approximate, but not actual, mandibular movement.